Weld seams are known to be a possible source of weakness in a welded structure. It is therefore common practice to inspect welds for signs of fatigue in order that any deterioration in the weld may be repaired before the weld, and possibly the structure of which the weld forms a part, fails.
Typically, welds are monitored for fatigue and signs of failure by carrying out manual inspections of the welds at pre-determined time intervals.
In some environments carrying out such inspections can be a costly exercise. For example, in the case of wind turbine towers, and in the case of offshore wind turbines the mono-piles on which they stand, it is necessary for personnel to enter the turbine tower and/or mono-pile. For off-shore wind turbines a special service vessel must be deployed to take the personnel out to sea. Further, personnel may only be deployed onto off-shore wind turbines when the sea conditions are favourable.
In an off-shore wind turbine the mono-pile is intended to be sealed against ingress of water. However, in practice water is found to penetrate the mono-pile. In such a scenario the mono-pile must be pumped free of water before inspection of the welds may begin or inspection must be performed by and ROV with the water in situ, or a diver inspecting visually from outside the mono-pile.
Whilst periodic inspection of welds may be adequate, the mono-piles and towers upon which wind turbines are mounted are subject to varying loads causing the mono-pile and tower to repeatedly bend. It is well understood that structures subject to cyclic loading are more likely to fail over time than structures subject only to static loads.
It would therefore be desirable to provide an apparatus and method that allows weld seams to be monitored constantly, rather than periodically. Further, it would be desirable to provide an apparatus and method that allows the weld seams of a structure to be monitored remotely.
It would also be desirable to provide an apparatus that not only provides for monitoring of the integrity of a weld seam, but also will protect the structure against ingress of matter through a failed weld seam.
The apparatus and method described herein will be useful not only in relation to wind turbine towers and mono-piles. There are many structures which have critical welds and which require monitoring, either due to their remote location or because they are older than their expected service life. For example, parts of oil rigs, pressure vessels, platform structures, etc.